The present embodiments relate generally to data transmission in communication systems and, more specifically, to methods and systems for control information transmission in networks and devices implementing carrier aggregation.
As used herein, the terms “user equipment” and “UE” can refer to wireless devices such as mobile telephones, personal digital assistants (PDAs), handheld or laptop computers, and similar devices or other User Agents (“UA”) that have telecommunications capabilities. In some embodiments, a UE may refer to a mobile, wireless device. The term “UE” may also refer to devices that have similar capabilities but that are not generally transportable, such as desktop computers, set-top boxes, or network nodes.
In traditional wireless telecommunications systems, transmission equipment in a base station or other network node transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an evolved universal terrestrial radio access network (E-UTRAN) node B (eNB) rather than a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment, and a packet-based network that uses such equipment can be referred to as an evolved packet system (EPS). Additional improvements to LTE systems and equipment may result in an LTE advanced (LTE-A) system. As used herein, the phrase “base station” will refer to any component or network node, such as a traditional base station or an LTE or LTE-A base station (including eNBs), that can provide a UE with access to other components in a telecommunications system.
In mobile communication systems such as the E-UTRAN, a base station provides radio access to one or more UEs. The base station comprises a packet scheduler for dynamically scheduling downlink traffic data packet transmissions and allocating uplink traffic data packet transmission resources among all the UEs communicating with the base station. The functions of the scheduler include, among others, dividing the available air interface capacity between UEs, deciding the transport channel to be used for each UE's packet data transmissions, and monitoring packet allocation and system load. The scheduler dynamically allocates resources for Physical Downlink Shared CHannel (PDSCH) and Physical Uplink Shared CHannel (PUSCH) data transmissions, and sends scheduling information to the UEs through a control channel.
To facilitate communications, a plurality of different communication channels are established between a base station and a UE including, among other channels, a Physical Downlink Control Channel (PDCCH). As the label implies, the PDCCH is a channel that allows the base station to control a UE during downlink data communications. To this end, the PDCCH is used to transmit scheduling assignment or control data packets referred to as Downlink Control Information (DCI) packets to the a UE to indicate scheduling to be used by the UE to receive downlink communication traffic packets on the PDSCH or transmit uplink communication traffic packets on the PUSCH or a Physical Uplink Control Channel (PUCCH) or specific instructions to the UE (e.g., power control commands, an order to perform a random access procedure, or a semi-persistent scheduling activation or deactivation). A separate DCI packet may be transmitted by the base station to a UE for each traffic packet/sub-frame transmission.
In a wireless communications network, it is generally desirable to provide high data rate coverage using signals that have a high Signal to Interference Plus Noise ratio (SINR) for UEs serviced by a base station. Typically, only those UEs that are physically close to a base station can operate with a very high data rate. Also, to provide high data rate coverage over a large geographical area at a satisfactory SINR, a large number of base stations are generally required. As the cost of implementing such a system can be prohibitive, research is being conducted on alternative techniques to provide wide area, high data rate service.
In some cases, carrier aggregation can be used to support wider transmission bandwidths and increase the potential peak data rate for communications between a UE, base station and/or other network components. In carrier aggregation, multiple component carriers are aggregated and may be allocated in a sub-frame to a UE as shown in FIG. 1. FIG. 1 shows carrier aggregation in a communications network where each component carrier has a bandwidth of 20 MHz and the total system bandwidth is 100 MHz. As illustrated, the available bandwidth 100 is split into a plurality of carriers 102. In this configuration, a UE may receive or transmit on multiple component carriers (up to a total of five carriers 102 in the example shown in FIG. 1), depending on the UE's capabilities. In some cases, depending on the network deployment, each component carrier can have a smaller bandwidth than 20 MHz or carrier aggregation may occur with carriers 102 located in the same band and/or carriers 102 located in different bands. For example, one carrier 102 may be located at 2 GHz and a second aggregated carrier may be located at 800 MHz.
In many networks, information describing the state or condition of one or more of the communication channels established between a UE and a base station can be used to assist a base station in efficiently allocating the most effective carrier resources to a UE. The state information is referred to as channel state information (CSI) and is associated with a particular channel or carrier established between the base station and the UE. The CSI provides information about the observed (by the UE) channel quality on a downlink carrier back to the base station.
Generally, the CSI is communicated to the base station within uplink control information (UCI). In some cases, in addition to the CSI, UCI contains Hybrid Automatic Repeat reQuest (HARQ) acknowledgment/negative acknowledgement (ACK/NACK) information in response to PDSCH transmissions on the downlink. Depending upon the system implementation, the CSI may include the following data as channel quality information: Channel Quality Indicator (CQI), Rank Indication (RI), and/or Precoding Matrix Indication (PMI). For LTE-A (Rel-10), there may be other types of channel quality information in addition to the Rel-8 formats listed above. Generally, the CQI assists the base station with selecting an appropriate modulation and coding scheme (MCS). The RI provides an indication as to whether the UE can support one or multiple spatial multiplexing layers, and the PMI provides information about the preferred multi-antenna precoding for downlink transmissions.
In an E-UTRAN Release 8 system, there are generally two approaches for transmitting UCI in a subframe as illustrated in FIGS. 2a and 2b. FIGS. 2a and 2b are illustrations of exemplary physical resource mapping for transmitting UCI within a PUCCH and a PUSCH resource, respectively. Generally, an RB is formed by a number of Resource Elements (REs). The REs may be arranged in twelve frequency columns and fourteen time rows (see FIG. 3, for example). Accordingly, each RE corresponds to a particular time/frequency combination. The combination of elements in each time row can be referred to as a Single Carrier—Frequency Division Multiple Access (SC-FDMA) symbol. Various types of data can be communicated in each RE or combination of REs. (In FIGS. 2a and 2b, elements 101, 103 and 104 each include a combination of REs.)
FIG. 2a illustrates the subframe configuration for transmission using the PUCCH and FIG. 2b shows a PUSCH configuration. Both figures show subframes that include two slots (Slot 0 and Slot 1) with frequency increasing from the bottom of the RB to the top. Both figures show a particular subframe n. At any time, a UE may only transmit UCI on either the PUCCH or PUSCH. As such, only a single one of the subframe configurations shown in either FIG. 2a or FIG. 2b can be transmitted by a UE at a particular time to maintain the single carrier property in uplink.
PUCCH resources are generally located at the edge of the system bandwidth and different frequency resource is used for Slot 0 and Slot 1 to achieve frequency diversity gain. Accordingly, in FIG. 2a, PUCCH block 101 is located at the top of the RBs, at the highest system bandwidth, and PUCCH block 103 is located at the bottom of the RBs, at the lowest system bandwidth. Generally, the precise PUCCH resource is configured or implicitly mapped using the PDCCH call control element (CCE) index. Both PUCCH resources 101 and 103 can be used to transmit UCI in the available PUCCH resources as long as the UE does not transmit using the PUSCH configuration (see FIG. 2b) in the same subframe.
Referring to FIG. 2b, if the UE is transmitting using the PUSCH in subframe n, the UCI information may be transmitted within the PUSCH. As shown in FIG. 2b, PUSCH 104 may occupy a central region of the available system bandwidth, with the UCI being included within PUSCH 104.
When transmitting the UCI within the PUSCH, the UCI is multiplexed into the uplink-shared channel (UL-SCH). FIG. 3 is an illustration of an exemplary multiplexing of UCI into the UL-SCH assuming an RB is scheduled for the PUSCH. As seen in FIG. 3, the coded CQI/PMI bits 110 can be located at the beginning of the available PUSCH resources before interleaving. To avoid data puncturing due to CQI or PMI transmission, the UL-SCH data is rate-matched to be transmitted with the remaining resources. The coded ACK/NACK bits 112 can be multiplexed with the UL-SCH data in the channel interleaver by puncturing symbols of the UL-SCH data. The location of HARQ ACK/NACK symbols 112 is generally next to the SC-FDMA symbols used as reference signals (RS) 114 to achieve the best channel estimation for HARQ ACK/NACK bits 112. Rank indication (RI) bits 116 can be located next to the HARQ ACK/NACK symbols in the time dimension, but unlike ACK/NACK, the UL-SCH data may be rate-matched to accommodate RI resources 116.
Generally, in a PUSCH transmission, the number of coded symbols for HARQ-ACK and RI is calculated using the following equation (1) (see, for example, TS 36.212 Section 5.2.4.1“3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (Release 8)”:
                              Q          ′                =                  min          ⁡                      (                                          ⌈                                                      O                    ·                                          M                      sc                                              PUSCH                        ⁢                                                  -                                                ⁢                        initial                                                              ·                                          N                      symb                                              PUSCH                        ⁢                                                  -                                                ⁢                        initial                                                              ·                                          β                      offset                      PUSCH                                                                                                  ∑                                              r                        =                        0                                                                    C                        -                        1                                                              ⁢                                          K                      r                                                                      ⌉                            ,                              4                ·                                  M                  sc                  PUSCH                                                      )                                              Equation        ⁢                                  ⁢                  (          1          )                    
In equation (1), O is the number of ACK/NACK bits or rank indicator bits, MscPUSCH is the scheduled bandwidth for PUSCH transmission in the current sub-frame for the transport block (expressed as a number of subcarriers in TS 36.211, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8)”), βoffsetPUSCH is an amplitude scaling factor for the PUSCH, and NsymbPUSCH-initial is the number of SC-FDMA symbols per subframe for initial PUSCH transmission for the same transport block given by NsymbPUSCH-initial=(2·(NsymbUL−1)−NSRS), where NSRS is equal to 1 if the UE is configured to send PUSCH and SRS in the same subframe for initial transmission or if the PUSCH resource allocation for initial transmission overlaps, even partially, with the cell specific SRS subframe and bandwidth configuration defined in Section 5.5.3 of TS 36.211, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8)”. Otherwise NSRS is equal to 0. MscPUSCH-initial, C, and Kr can be obtained from the initial PDCCH for the same transport block. Accordingly, equation (1) defines a minimum number of HARQ ACK/NACK bits to be encoded within a PUSCH subframe.
Generally, the actual number of coded symbols for channel quality information (CQI and/or PMI) can be determined using equation (2) (see, for example, TS 36.212 in Section 5.2.4.1“3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (Release 8)”):
                              Q          ′                =                  min          ⁡                      (                                          ⌈                                                                            (                                              O                        +                        L                                            )                                        ·                                          M                      sc                                              PUSCH                        ⁢                                                  -                                                ⁢                        initial                                                              ·                                          N                      symb                                              PUSCH                        ⁢                                                  -                                                ⁢                        initial                                                              ·                                          β                      offset                      PUSCH                                                                                                  ∑                                              r                        =                        0                                                                    C                        -                        1                                                              ⁢                                          K                      r                                                                      ⌉                            ,                                                                    M                    sc                    PUSCH                                    ·                                      N                    symb                    PUSCH                                                  -                                                      Q                    RI                                                        Q                    m                                                                        )                                              Equation        ⁢                                  ⁢                  (          2          )                    
In equation (2), O is the number of CQI bits, L is the number of cyclic redundancy check (CRC) bits given by
  L  =      {                                        0                                              O              ≤              11                                                            8                                otherwise                              ,      QCQI=Qm·Q′ and [βoffsetPUSCH=βoffsetCQI]; respectively, where βoffsetCQI may be determined according to TS 36.213, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 8)”. If a rank indicator is not transmitted, then QRI=0. MscPUSCH-initial, C, and Kr can be obtained from the initial PDCCH for the same transport block.
In E-UTRAN Release 8 systems, multiple applications supported in a UE can have different quality of service (QoS) requirements. For example, VoIP service may require a smaller delay requirement, while file transfer protocol (FTP) applications may be more tolerant of delays. To support different QoS, different radio bearers may be configured and each bearer may be associated with a particular QoS.
On the uplink channels, each radio bearer maps onto a separate logical channel. FIG. 4 is an illustration showing the mapping from various uplink radio bearers, to uplink logical channels, to uplink transport channels, and, finally, to uplink physical channels. Referring to FIG. 4, Signaling Radio Bearers (SRBs) 150 can carry control-plane signaling messages. For example, SRB0 may correspond to the Common Control CHannel (CCCH) that is used only when a UE does not have a regular connection with a DCCH (Dedicated Control CHannel). The other two SRBs 150 may map to separate DCCHs after a connection has been established, for example. SRB1 can be used to carry control-plane messages originating from radio resource configuration (RRC), and SRB2 can used to carry encapsulated control-plane messages originating from the non-access stratum (NAS). Data Radio Bearers (DRBs) 152 can carry user-plane traffic. A separate Dedicated Traffic CHannel (DTCH) may be set up for each active DRB.
In FIG. 4, each of the uplink logical channels map to the UL-SCH 154 at the transport channel level, which in turn maps to the PUSCH 156 at the physical channel level. Separately, the Random Access CHannel (RACH) 158 transport channel maps to the Physical RACH (PRACH) 160 for performing random accesses, and the PUCCH physical channel 162 carries physical layer signaling to the base station.
Additionally, the UE may transmit medium access control (MAC) control elements (MAC CE) on the uplink channel to communicate control signaling to the base station. MAC control elements can be short (e.g., a few bytes) signaling messages that are included within a MAC Protocol Data Unit (PDU) that is transmitted on the uplink to the base station. For example, Rel-8 MAC control elements may include a Cell Radio Network Temporary Identifier (C-RNTI) MAC CE, a Buffer Status Report (BSR) MAC CE, and a Power Headroom Report (PHR) MAC CE.
MAC CEs (if appropriate) may first be scheduled into any new uplink transmission allocation. Generally, MAC CEs have a higher priority than logical channel traffic (e.g., from a DCCH or DTCH), with the exception of a Padding BSR. UL-CCCH traffic (e.g., from SRB0) may also have higher priority than MAC control elements.
In Release 8, UCI can be transmitted on either the PUCCH or PUSCH depending on whether PUSCH resources for UL-SCH transmission are scheduled and available. In newer network implementations providing carrier aggregation, however, a UE may be scheduled to transmit PUSCH on multiple uplink carriers simultaneously to increase the peak data rate. In some network implementations, however, only a single carrier may be allocated for UCI transmissions within the PUCCH from a UE. In that case, a single UE-specific UL component carrier (CC) is configured semi-statically for carrying PUCCH UCI from a UE. In such an implementation, only one UL CC is configured to transmit PUCCH for UCI transmission even though multiple UL CCs are configured to transmit data with PUSCHs. This may reduce UE battery power consumption by turning on only a single carrier for control signaling. In addition, it may be beneficial to reduce the control signaling overhead because only a single transmit power control (TPC) command is sufficient to control PUCCH power.
In some cases, simultaneous transmission of UCI and data may also be supported in a network. In that case, UCI may be transmitted on the PUCCH along with PUSCH for data transmission. In such an implementation, the single carrier property can be relaxed with the introduction of clustered Discrete Fourier Transform-Spread Orthogonal Frequency Division Multiplexing (DFT-S-OFDM), for example. In such an implementation, however, simultaneous transmission of PUCCH and PUSCH may cause larger radio emissions due to the inter-modulation between PUCCH and PUSCH especially within a carrier—it is likely that the transmit power difference between PUCCH and PUSCH is relatively large due to the different data rates.
Generally, in newer networks, the payload of UCI is expected to be larger than that of Release 8 because LTE-A UEs may support DL transmission on multiple DL carriers because CQI/PMI/RI feedback for each of the available carriers will be communicated to the base station by the UE and HARQ ACK-NACK feedback for each of the scheduled carriers will be required. As such, the payload of UCI could increase linearly with the number of active DL carriers. For example, in Release 8, the number of HARQ-ACK bits is generally 1 bit or 2 bits for Frequency Division Duplexing (FDD) and 1-4 bits for Time Division Duplexing (TDD). Table 1 shows the required bits for HARQ-ACK data depending upon the number of scheduled downlink carriers and the number of code words. The values are calculated assuming ACK, NACK and DTX indications are required for each carrier because PDCCHs are separately transmitted to schedule PDSCH on multiple carriers. In the case of two code words, five indication values are required as ACK/NACK for first codeword, ACK/NACK for second codeword and DTX for PDCCH misdetection. That is, the UE needs to be able to signal the following five different states for the case of two code words (A=ACK, N=NACK): (A,A), (A,N), (N,A), (N,N), and DTX. As shown in Table 1, as the number of carriers increases, so does the numbers of bits required for each codeword, whether the codeword is a double or single codeword.
TABLE 1Number of carriers2345Two code words┌log2 5N − 1┐571012Single codeword┌log2 3N − 1┐3578
A result of an increase in UCI data to be transmitted by the UE is to reduce the available UL-SCH resources for data transmission due to rate matching or puncturing in a transmission. This is particularly true for HARQ-ACK transmissions, where puncturing may be prevalent. To minimize the reduction of the available UL-SCH resources due to the UCI, the base station can increase the PUSCH resources. If, for example, UCI is transmitted within the PUSCH and the PUSCH resource is dynamically scheduled for the initial transmission the PUSCH resources can be increased to accommodate the resources for the UCI transmission. However, if UCI needs to be transmitted within the PUSCH for the re-transmission of UL-SCH data or semi-persistently scheduled PUSCH resources, it may be difficult to increase the PUSCH resources. In this case, it may be necessary to retransmit the data because the transmission with the UCI may not be successfully received due to the puncturing losses caused by the UCI transmission. The increased number of transmissions may not be detrimental if the data is not delay-sensitive, e.g., FTP or TCP IP data. But the increased number of transmissions may negatively affect the performance of delay-sensitive data, e.g., VoIP or MAC signaling (e.g., MAC control element), or RRC signaling messages that include measurement reports, or other high priority data traffic.